October 2011
ICS 77.140.50
Supersedes DIN 693522010-O1
Cold bending of flat rolled steel, English translation of DIN 6935:2011-10 Kaltbiegen__von Flacherzeugnissen aus Stahl, Englische Ubersetzung von DIN 6935:2011-10 Cintrage a froid des produits plats en acier, Traduction anglaise de DIN 6935:2011-10
Document comprises 13 pages
Translation by DIN-Sprachendienst. In case of doubt, the German-language original shall be considered authoritative.
DIN 6935:2011-10
A comma is used as the decimal marker.
Contents Page Foreword ....................................................................................................................................................... .. 3 1
Scope ............................................................................................................................................... .. 4
2
Normative references ..................................................................................................................... .. 4
3 3.1 3.2
Bending radii ................................................................................................................................... .. 4 General ............................................................................................................................................. .. 4 Bending angle 04 and thickness s .................................................................................................. .. 4
4
Key to materials .............................................................................................................................. .. 6
5
Minimum leg length ........................................................................................................................ .. 6
6
Permissible deviations for angular positions on bending sections .......................................... .. 6
7
Calculation of developed lengths ................................................................................................. .. 7
8
Representation and position of bend lines for developments ................................................. .. 10
9
Dimensioning and calculation of developed lengths (examples) ............................................ .. 10
10
Development and marking of bend line position (example) .................................................... .. 12
Bibliography ............................................................................................................................................... .. 13
2
DIN 6935:2011-10
Foreword This standard has been prepared by Working Committee NA 026-00-03 AA Stanzteile of the Normenausschuss Federn, Stanzteile and Blechformteile (NAFS) (Springs, Stamped Parts and Moulded Parts Standards Committee). For more information on NAFS, visit our website at www.nafs.din.de. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. DIN shall not be held responsible for identifying any or all such patent rights. Amendments This standard differs from DIN 6935:2010-01 as follows: a)
the scope has been updated;
b)
normative references have been updated;
c)
figures have been provided with titles;
d)
Clause 3 has been changed;
e)
Tables 1 to 3 have been revised;
f)
the standard has been editorially revised.
Previous editions DIN 6935: 1958-01, 1967-05, 1969-05, 1975-10, 2010-01
3
DIN 6935:2011-10
1
Scope
This standard applies for bent parts made of flat steel products for application in steel construction and mechanical engineering. For standards on flat steel products, see DIN EN 10025-2.
2
Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. DIN 250, Radii DIN EN 10025-2, Hot-rolled products of structural steels — Part 2: Technical delivery conditions for non-al/oy structural steels
3 3.1
Bending radii General
When bending flat rolled steel such as sheets, strips, wide flats etc., the rolling direction shall be taken into consideration, since bending should be carried out transverse to the rolling direction, because this is more suitable for bending. The suitability of the rolled steel for bending shall be agreed with the manufacturer’s works when ordering. To guarantee bending suitability, the rolled surface shall be flawless and the sheared edges straight. For flat rolled steel, the sheared edges on the outside of a bend shall also be de-burred at the bending location to prevent cracks from spreading from the cut edges.
3.2
Bending angle a and thickness s
The bending angle a can have any value between 0° and 180°. Thickness s decreases by approximately 20 % in the rounded portion (see Figure 1).
1;).
<
-_-. .
-'1?‘
I
I 1
~'= E
Key r Bending radius 0: Bending angle fl Opening angle Figure 1 — Bending radius (notation) To obtain uniform bends on bending rails, it is recommended that only bending radii from the series below be selected. The values printed in bold are to be preferred. 4
DIN 6935:2011-10
Dimensions in millimetres
IIIEEHHIHHEHEEEEEM These bending radii comply with the radii according to DIN 250. Table 1 gives the minimum permissible bending radii to be chosen for given sheet thicknesses and materials and for the applicable bending machines. The indicated values apply for bending angles as 120°. For bending angles 04> 120° the next higher value in the table shall be used, e.g. if sheets of S 275 JR according to DIN EN 10025-2 are to be bent transverse to the rolling direction, with a thickness S = 6 mm, the minimum permissible bending radius is r : 10 mm for as 120° and r = 12 mm for 04> 120°. Table 1 — Minimum permissible bending radius r Dimensions in millimetres For
Minimum permissible bending radius r for thicknesses 5
bending
Steel grades
transverse or parallel to the rolling
Up
to
Over
1
1
Over Over Over Over
1,5
2,5
3
4
upto upto upto upto upto
Over
Over
Over
5
6
7
upto
upto
upto
Over Over Over Over Over Over 8
10
12
14
16
18
upto upto upto upto upto upto
direction
1,5
2,5
3
4
5
6
7
12
14
16
18
20
S 235 .R S 235 S 235 .2
Transverse
1,6
2,5
3
5
6
8
"
20
25
28
36
40
Parallel
1,6
2,5
3
6
8
’O
25
28
32
40
45
S 275 .R S 275 S 275 .2
Transverse
2
3
4
5
8
‘O
25
28
32
40
45
Parallel
2
3
4
6
10
’2
32
36
40
45
50
S 355 .R S 355 S 355 .2
Transverse
2,5
4
5
6
8
’O
25
32
36
45
50
Parallel
2,5
4
5
8
10
’2
32
36
40
50
63
B-0
B-0
B-0
Table 2 gives permissible deviations for minimum bending radii which are to be expected for various sheet thicknesses and materials. Table 2 — Permissible deviations for minimum bending radii r Dimensions in millimetres Steel grades
Permissible deviations for minimum bending radii r for thicknesses s Up to 3
Over 3 up to 8
Over 8 up to 20
S 235 R S 235 O S 235 2
+0,5 I3»
O
S 275 S 275 S 275 |\>o;U
+0,8
+1,5
I3»
O
0
S 355 S 355 S 355 |\>o;U
+1
+2
+3
0
0
0
+1
+1,5 0 +2
5
DIN 6935:2011-10
4
Key to materials
Table 3 provides examples of materials for which suitability for cold bending, cold flanging and cold curling is guaranteed, taking into account the minimum permissible bending radii specified in Table 1. Table 3 — Key to materials (examples) Steel grade with a minimum tensile strength °‘
TYP° °f 519°‘ Hot-rolled products of structural steels according
Over 360 MPa
Over 430 MPa
Over 510 MPa
up to 510 MPa
up to 580 MPa
up to 680 MPa
S 235 JR
S 275 JR
S 355 J2
to DIN EN 10025-2
5
Minimum leg length
When mechanically bending sections of sheet metal, the leg length b is approximately 4 - r (see Figure 2).
‘Q
J
1 Figure 2 — Minimum leg length (notation)
6
Permissible deviations for angular positions on bending sections
Table 4 provides an overview of permissible deviations of bending angles in relation to leg lengths. Table 4 — Permissible deviations of angular positions Dimensions 'n millimetres Leg lengths a and b (wherethe ShQfte|'|eg length is regarded as the nominal length)
E:;'L‘i'§;':L°gfIe°‘;'°t'°"° °f
6
Upto 30
Over 30 up to 50
Over 50 up to 80
Over 80 up to 129
Over 120
+ 2°
+ 1° 45'
+ 1° 30'
+ 1° 15'
+ 1°
DIN 6935:2011-10
ti-
?
I
I
I -
El
Figure 3 — Permissible deviations for angular positions (notation) Values apply for a ratio up to r : s : 4. For a larger (r : s) ratio, a larger deviation due to spring back is to be expected (see Figure 3).
7
Calculation of developed lengths
Developed length:a+b+v. Depending on the value of the bending angle, v varies and represents a compensating value which, at an opening angle ,6 of 0° up to 65° (calculated value 65° 24' 30"), can be negative or positive, and at an opening angle over 65° can only be negative. Developed lengths shall be rounded up to the nearest full millimetre.
Compensating value u = 1; - {I810;0_ '8) (
2 k) — 2 (r + s)
4.5
RI .‘t~
~aIFI“
--``,`,`,,,,`,`,,,`,``,,```,`,,`-`-`,,`,,`,`,,`---
Opening angle ,60° up to 90° (1)
§§'§ 3
Figure 4 — Opening angle ,6 0° up to 90° (notation)
7
DIN 6935:2011-10
Opening angle ,690° up to 165° Compensating value 0 : 1c- I800 _ '8 180°
S k — 2 (r + s)- tan E 2 2
(2)
/I?
ml I
0.
flu
Sggl’?
-
Figure 5 — Opening angle ,690° up to 165° (notation)
Opening angle ,6165° up to 180° Compensating value 0 : 0 The values for 0 are negligibly small in this case and sufficiently accurate for practical applications.
,5’ 5 A A I“
.
b
- —-in-I —|-I|——
El
_'Ii__
Figure 6 — Opening angle ,6165° up to 180° (notation)
Correction factor k to determine the cut lengths of bent workpieces The correction factor k gives the deviation of the position of the neutral line; and can be calculated as follows:
k:0,65+lIg£ 2
s
(3)
or can be taken from the following graphical representation in Figure 7, which represents the equation. For r : s > 5, Equation (3) is no longer valid so that k: 1 applies.
8
DIN 6935:2011-10
if
I 1,2’ 1,1 1 0,9 0,8 0,? 0,6
—
—
0,5 0,11 L 0,3
I
0,2 0,1
0
-—
0
"
2
3
L»
5
Pl’ 5
Figure 7 — Graphical representation of correction factor If only minimum requirements are set for the determination of cut lengths, rounded values as grouped together in Table 5 may be used for the correction factor k. Table 5 — Correction factor k, rounded values Inte_maI bendIn9' radius r as a function ofS sheet thickness C orrec t'ion fac t or k (rounded values)
.
Over 0,65
Over 1
Over 1,5
Over 2,4
up to 1
up to 1,5
up to 2,4
up to 3,8
0,7
0,8
0,9
Over 3,8
Rat|O r ' s
'
0,6
1
For any value for ,6, r and s, the corresponding compensating values 0 can also be identified by the use of the correction factor ktogether with the graphical representations of factors in DIN 6935, Supplement 1. For calculated compensating values 0 for several opening and bending angles based on the above formula for correction factor k, see DIN 6935, Supplement 2.
9
DIN 6935:2011-10
8
Representation and position of bend lines for developments
The bend line indicates the middle of the bending radius and shall be represented by a thin continuous line. The position of the bend line results from the abutting leg lengths a and b, with half of the positive or negative compensating value 0 taken into account (see Figure 8).
.-£l+0+v
0+»-'72
I
W2 +3
Figure 8 — Representation and position of the bend line (notation) Developments shall only be explicitly drawn if the shape of the cut sheet is not unambiguously determined by dimensioning and indication of the bend line.
9
Dimensioning and calculation of developed lengths (examples)
All dimensions in millimetres EXAMPLE 1 Material: S 235 JR Sum of leg lengths .. ..................... .. 50 + 200 + 80 = 330 FOI‘,B=9()°,r= 6,s=4then .......... ..v=—8,26 FOI‘,B=9()°,r=2(),s=4’[hen .......... .. v=—13,44=—21,7 Developed length ........................................ .. 308,3 z 309 Dimensions in millimetres 200
s
-;>,_,.
Q35»
1+
Figure 9 — Example 1 (notation)
10
E
--``,`,`,,,,`,`,,,`,``,,```,`,,`-`-`,,`,,`,`,,`---
_
DIN 6935:2011-10
EXAMPLE 2
Material: S 235 JR Sum of leg length .. ....................... .. 50+ 170+246+50=516 For,6= 9()°,r=20,s=12’[hen ......... ..v=—25,41 For,6= 45°,r=2(),s=12’[hen .......... ..v= —6,12 For,6= 135°, r: 32, S: 12 then ......... .. 0: —7,25=—38,78 Developed length ........................................ ..
477,22 z 478
Dimensions in millimetres
_l {
3
,1: /9 L-.1
A
1;;
935°.
bf].
9 I?
8 ‘fa’
_l 5U
Figure 10 — Example 2 (notation)
11
DIN 6935:2011-10
10 Development and marking of bend line position (example) Material: S 355 J2 All dimensions in millimetres Development: Sum of leg lengths .. ........................... .. 45 + 50 + 32 = 127 For,6= 45°,r=1(),s=5’[hen ......... ..v= —1,72 For,6=135°,r=10,s=5then ......... ..v= —3,00 = —4,72 Developed length ........................................ ..
= 122,28 ~ 123
Dimensions in millimetres
I-+5
I 1
<0 FR 111 J;
= --II‘ --I.|'
I
lip
32
=5? 5'35.
rn i.""~I ,_ II
E .l
I
Figure 11 — Development and marking of bend line position (example) (notation) Position of bend lines: For leg length = 45, ,6: 45°, r= 10, s = 5 and 0 = —1,72 then 45—% : 45 — 0,86 : 44,14 ~ 44 For leg length = 32,,6=135°,r=10,s= 5 and 0 =—3 then 32 —%= 32 — 1,5 = 30,5 ~ 31
12
DIN 6935:2011-10 Bibliography
DIN 1623, Cold rolled strip and sheet — Technical delivery conditions — General structural steels DIN 6935 Supplement 1, Cold bending of flat rolled steel — Supplement 1: Factors determining the correction value 0 for calculating length of flats prior to bending DIN 6935 Supplement2, Cold bending of flat steel products — Supplement 2: Calculated compensating valuesv DIN 59200, Flat products of steel — Hot rolled wide flats — Dimensions, mass, tolerances on dimensions, shape and mass DIN EN 10048, Hot-rolled narrow steel strip — Tolerances on dimensions and shape DIN EN 10058, Hot rolled flat steel bars for general purposes — Dimensions and tolerances on shape and dimensions DIN EN 10131, Cold rolled uncoated and zinc or zinc-nickel electrolytically coated low carbon and high yield strength steel flat products for cold forming — Tolerances on dimensions and shape DIN EN 10139, Cold rolled uncoated mild steel narrow strip for cold forming — Technical delivery conditions DIN EN 10140, Cold rolled narrow steel strip — Tolerances on dimensions and shape
13
